Well heater



May 21, 1957 Fil ed May 3, 1954 C. A. CARPENTER WELL HEATER 2Shets-Sheet 1 Avnwra May 21, 1957 c. A. CARPENTER WELL HEATER 2Sheets-Sheet 2 Filed May 5; 1954 United States Patent WELL HEATERClayton A. Carpenter, La Hahra, Califi, nssiguor to Union ()il Companyof California, Los Angeles, 023222., a corporation of CaliforniaApplication May 3, 1954, Serial No. 427,188

13 Claims. (Cl. 166-61) This invention relates to an apparatus forheating current is supplied through cables running down the well here orthrough parts of the well structure itself, e. g., the well tubing,casing or sucker rods. In most instances it has been found that bestresults in heating wells are attained by heating more or lesscontinuously at a relatively low rate of power consumption and whilepumping oil from the well. Accordingly, the most desirable form ofheater is constructed so as to comprise an oilconducting conduit whichcan be coupled into and made a part of the tubing string and throughwhich oil can be pumped to the earths surface during heating. lowever,the structural limitations of this type of heater are such thatdifficulty is bad in providing suflicient heating capacity withoutmaking the heater unduly large. Further difficulties are had in suitablyinsulating the turns of the resistance heating coil and in providingmeans for mounting the same within the heater so as to allow forexpansion upon heating. The various heater designs which have beenproposed to overcome these difiiculties have involved complicatedarrangements of electrical and thermal insulation, spring mounted coilforms, liquid circulating means, baffles, sealing means, etc., all ofwhich unduly increase the cost of the heater and render it dithcult toconstruct and maintain.

The well heater provided by the present invention is of extremely simpledesign and construction and has been found to be substantiallytrouble-free. Substantially no electrical or thermal insulation isemployed, and the component parts can be mass-produced at very low cost.Assembly and maintenance costs are reduced to a minin, yet the heaterhas been found to operate with maximum efiiciency. In brief, said heatercomprises an int-perforate oil-conducting conduit having a cylindricalshell concentrically disposed around it and sealed thereto by annularend closures. The electrical resistance heating element is mounted inthe annular space between the central conduit and the shell, and takesthe form of a serpentine inscribed on an imaginary surface which extendslongitudinally within said annular space and is spaced away from theconduit and the shell, said serpentine having relatively long traversessubstantially parallel to the longitudinal axis of the conduit. Theheating element is supported in this position by a plurality ofinsulated supports attached to the conduit, and each longitudinaltraverse of the heating element is clamped at approximately itsmid-point so as to allow for expansion both upwardly and downwardly uponheating. In a 'ice preferred form of the de cc, one end of th tingelement is internally grounded to the central CUl tat and the other endis connected to an insulated cable w ich passes through the walls of theheater via a fluid-tight seal and runs to the earths surface and asource of electric current.

Referring now to the several figures of the accompanying drawings whichform a part of this application and in which like numerals designatelike parts:

Figure 1 represents a top plan view of one form which the present Wellheater may take;

Figure 2 represents a vertical elevation, partly in section, taken alongline 2-2 of the heater shown in Figure 1;

Figure 3 is a fragmentary plan view of one type of member for supportingthe heating element within the body of the heater;

Figure 4 is a fragmentary sectional elevation of one of said members andone of the insulators associated therewith;

Figure 5 is a vertical elevation of one of the loops of resistance wirewhich go to rnalre up the heating element of the present heater;

Figures 6-9 are plan and elevation view of alternative means forsupporting the heating element within the body of the heater; and

Figure 10 is a partial vertical elevation of a well heater constructedin accordance with the invention and in which a particulate solid isemployed as a heat-conducting insulant.

Referring now to Figures 1 and 2, the heater therein illustratedcomprises a central oil-conducting conduit 11, the upper end of which isthreaded to engage a section of well tubing and the lower end of whichis perforated, as by slots 12, to allow oil to enter the conduit and bedrawn upwardly therethrough by the well pump, not shown. Annular upperand lower end closures 13 and 14, respectively, are welded to conduit 11as shown and form a fluid-tight seal therewith. Cylindrical shell 15 iswelded around the peripheries of closures 13 and 14, and togethertherewith forms a fluid-tight enclosure concentrically disposed aroundconduit 11. Triangular Webs 16 are welded to conduit 11 and the upperside of upper closure 13 to provide rigidity to the assembly.

Within the enclosed space formed by shell 15 and closures 13 and 14, aplurality of supporting members taking the form of annular rings 17 areaflixed, as by welding, in spaced relationship along the length ofconduit 11 and in planes perpendicular to the axis thereof. Said ringsare usually spaced about 35 inches apart. Each of said rings is providedwith a concentric row of perforations 17a extending through its opposedfaces, and each perforation carries a spool-shaped electrical insulator18. The rings are so aligned radially that straight lines parallel tothe longitudinal axis of conduit 11 can be drawn through the respectiveinsulators. The heating element 19 is formed of bare resistance wire,preferably Nichrome, threaded through holes 20 in insulators 18 so thatit takes the overall form of a serpentine longitudinally inscribed on animaginary cylinder coaxially disposed in the annular space betweenconduit 11 and shell 15. At approximately its mid-point, eachlongitudinal traverse of the heating element is fitted with upper andlower clamps 21 and 22, respectively, disposed on opposite sides of aninsulator. Said clamps may take the form of simple sleeves which arecrimped on the wire so as to prevent it from sliding within longitudinalopening 20 in insulator 18. Each traverse is thus fi-xed atapproximately its mid-point with respect to conduit 11, and upon heatingthe heating element is free to expand both upwardly and downwardly. Oneend of heating element 19 is electrically grounded to conduit 11 atterminal 23, and the other end is connected to insulated power cable 24by a suitable connector 25. Cable 24 passes through upper closure 13 andis supported exteriorly by a relatively short length of rigid electricalconduit 26. The latter terminates in cap 27 which is welded to centralconduit 11. Filler hole 28, which is normally closed by a plug 29,extends through upper closure 13 and provides a means for filling theheater with a particulate solid or a liquid as is hereinafter more fullyexplained.

Referring now to Figures 3 and 4 which illustrate certain details in theconstruction of a preferred means for supporting the heating elementwithin the body of the heater, said means takes the form of a pluralityof flat rings each having its outside diameter slightly less than theinternal diameter of shell and its inside diameter slightly larger thanthe outside diameter of conduit 11. In assembling the heater, the ringsare slipped over conduit 11, and tack-welded in place more or lessequally spaced along the length of conduit 11. Each of the rings carriesa series of radially spaced openings 17a drilled or punched with theircenters on a circle drawn between the inner and outer edges of the ring.The diameter and location of openings 17a are preferably such that theirouter edges extend to within a relatively short distance, say /8 inch,from the outer edge of the ring. Insulators 13 are formed of anelectrical-insulating material and must be capable of withstandingrelatively high temperatures. Ceramic materials, e. g. porcelain, glass,steatite, etc, are eminently suitable. Each insulator takes the form ofa relatively fiat spool, or a cylinder .with a peripheral groove, havingan axial hole which is slightly larger than the diameter of resistancewire 19 so that the latter is free to slide therein. The diameter ofeach insulator is just slightly less than that of openings 17a in ring17. Each insulator is afiixed to ring 17 by centering the insulator inperforation 17a and then applying pressure to the outer edge of the ringat a point closely adjacent to opening 17a, thereby permanentlydeforming the opening and causing its edge to fit within the peripheralgroove of the insulator. After the insulators have been so installed,the periphery of the ring will have a scalloped appearance, as shown inFigure 3, by reason of its having been deformed at the outer edge ofeach opening 17a. This manner of assembling the insulators on the ringhas proved very satisfactory in practice. If desired, however, two-piecelead-through insulators may be employed. It is usually most convenientto assemble the insulators on the rings as described prior to afixingthe latter to the central conduit, and when so afiixing the rings theyshould be carefully aligned so that the insulators on'successive ringsline up in straight lines substantially parallel to the axis of conduit11.

As previously stated, the heating element 19 is composed of bareresistance wire looped back and forth parallel to the axis and upon thesurface of an imaginary surface longitudinally disposed between conduit11 and .shell 15. Such element is readily constructed in place bybending suitable lengths of resistance wire into the form of a U asshown in Figure 5, and threading each arm of the U through the axialholes in adjoining insu- .lators on successive supporting members 17.The free ends of the U are then bent outwardly and are clipped off as atin Figure 5. A second U-shaped piece of resistance wire is threadedthrough the next adjoining two rows of insulators, and the open ends arebent outward- 1y as before. By welding together the outwardly bent endsof adjacent wires, as at 31 in Figure 1, the desired serpentineconfiguration will be obtained.

Referring now to Figures 6 and 7, which are elevation and plan view,respectively, illustrating the aforementioned spider arrangement, eachspider comprises a hub portion from which arms 41 extend radially. Eachof arms 41 terminates in a boss 42 having a longitudinal opening inwhich is carried a sleeve 43 constructed of an electrical insulatingmaterial such as porcelain. The spider is affixed to central conduit 11as by welding at 44. The resistance wire which forms heating element 19passes through sleeves 43, and is free to slide therein as previouslyexplained.

Referring now to Figures 8 and 9, which are elevation and plan views,respectively, illustrating the use of standoff insulators to support theheating element, a series of such insulators is shown extending radiallyfrom central conduit 11 in the same plane. Each insulator consists of ametallic base portion 50, which threads into suitable threaded openingsin conduit 11, and an insulator portion 51 which is composed of anelectrical insulating material such as porcelain and which threadedlyengages the base portion as shown. A longitudinal hole is provided nearthe outer end of each insulator portion 51 to receive heating element 19in sliding engagement.

As will be apparent to those skilled in the art, various modificationsof the above-described design may be made without departing from thescope of the invention. Thus, the supporting means for the heatingelement may take various forms other than the flat perforated ringsillustrated in the drawing and described above, e. g., they may take theform of spiders spaced along the conduit and carrying insulators at theend of each radial arm thereof, or they may comprise stand-offinsulators radially mounted on the central conduit in planes spacedalong the length thereof.

Also, various-types of sealing means may be employed for conducting theelectrical supply cable through the walls of the heater, and the heatingelement may be arranged so as to accommodate three-phase current. Ifdesired, the electric current may be fed to the heating element entirelyby supply cables running through the well bore rather than by thegrounded system illustrated. According to one modification, a groundedsystem is employed but the ground connection is made via the plug 29 inthe filler hole 28 so that by removing said plug the heating element isun-grounded and its resistance to ground can be determined in testingfor short-circuits.

As previously stated, filler hole 28 is provided in case -it is desiredto improve the transfer of heat from the heat- .with a heat transfermedium. Such medium may take the form of a heat-conductingelectrical-insulating liquid, e. g., the mixture of diphenyl anddiphenyloxide known as Dowtherm, as disclosed in the co-pendingapplication of James M. Covington, Serial No. 255,961 filed November 13,1951, or it may be a heat-conducting electrical-insulating particulatesolid, e. g., silica sand, as disclosed in my co-pending application,Serial No. 428,753 filed May 10, 1954. Mixtures of solids and liquidsmay also be employed. Figure 10 shows the device of Figure 2 filled witha body of such a particulate solid 60 in contact with heating element19, central conduit 11, and shell 15.

It will further be apparent that well heaters of the pres- .ent type canreadily be constructed of any desired size .of resistance wire to beadvantageously disposed in a minimum of space. The elimination ofinternal insulation also contributes to ease and economy of constructionand maintenance.

.consists of a 121 /2" length of 4.5" I. D. tubing. The bottom closureis machined from 0.675" hot-rolled steel,

'whereas the upper closure is similarly made from 0.75

steel. Thirty supporting rings, punched from 16 ga. hotrolled steel, arespaced about 4" apart along the central conduit within the body of theheater, and each ring has 18 equally spaced 0.5" holes punched aroundits circumfere'nce on a 3.5" diameter. The insulators are ceramic, 0.5"high and 0.5" in diameter, and have a .032" deep groove .094 wideinscribed around their peripheries. The insulators are mounted on therings by deforming the outer edge thereof as herein described. Theheating element is composed of U-shaped lengths of #12 Nichrome wirethreaded from the bottom through adjacent insulators on each supportingring, and then bent outwardly and welded to the adjoining length ofNichrome above the upper-most ring. A total of about 180 of Nichrome isemployed, giving a cold resistance of about 18.5 ohms. Each re sistancewire is secured at its approximate mid-point by crimping a short metalsleeve thereon on each side of the insulator which is located at aboutthe mid-point of the heater. One terminal of the heating element isbrazed to the central conduit and the other is connected to asingle-conductor power cable which is passed through the upper closurevia a fluid-tight seal as herein described. The heater is filled to alevel within about 2" of the top with dry 30- to IOO-mesh quartz sandintroduce through an 0.375 hole in the upper closure. A heater soconstructed has a nominal power rating of about 7.5 kw. at a surfacesupply voltage of about 385 volts A. C.

Operation of the present type of heater is no different from that ofprior practice, and it is ordinarily desirable that the heater beoperated more or less continuously with relatively low power consumptionduring pumping. Usually, the heater is located at the bottom of thetubing string, i. e., below the well pump, and may be positioned in thewell bore so as to transfer heat to the oil-producing formation eitherthrough the 'oil pool at the bottom of the well or through the gas phaseabove said pool. In some instances it is advantageous to heat and pumpwhile maintaining a substantial back-pressure on the well. As stated,the heater is usually operated on alternating current, 220-650 volt A.C. being commonly employed, although direct current may also beemployed. Usually it is desirable that the heater be of such capacityand be operated at such a power level that between about 0.02 and about2.0 kilowatts are dissipated in the form of heat per foot of formationsubjected to heating.

Other modes of applying the principle of my invention may be employedinstead of those explained, change being made as regards the elements ormeans employed provided the device stated by any of the followingclaims, or the equivalent of such stated device, be obtained.

1, therefore, particularly point out and distinctly claim as myinvention:

1. An electric heater for use in oil wells comprising an imperforateconduit adapted to be coupled to the well tubing; a coaxial tubularshell of substantially larger diameter than said conduit; spaced annularclosures forming a fluid-tight seal between said conduit and said shell;an electrical resistance heating element disposed within the annularspace between said conduit and said shell in the form of a serpentineinscribed on an imaginary surface extending longitudinally within saidannular space and in spaced relationship to said conduit and said shell,the longitudinal traverses of said serpentine being substantiallyparallel to the longitudinal axis of said conduit; electricallyinsulated means for holding said heating element so disposed within saidannular space, said means being supported on said conduit at spacedintervals and engaging the longitudinal traverses of said heatingelement in sliding relationship; means for ailixing said heating elementwith respect to said conduit at approximately the mid-points of thelongitudinal traverses of said heating element; and electricallyconductive means for supplying electric current to said heating elementfrom an exterior source.

2. A well heater in accordance with claim 1 wherein the saidelectrically conductive means comprises means for electricallyconnecting one end of said heating element to said conduit and at leastone insulated electrical conductor electrically connected to saidheating element and passing to the exterior of the heater via afluid-tight seal.

3. A well heater in accordance with claim 1 containing a particulateheat-conducting electrical-insulating refractory solid in the annularspace between said conduit and said shell in contact with said heatingelement, said conduit and said shell.

4. A well heater in accordance with claim 1 wherein the said means forsupporting the heating element comprises a plurality of relatively flatrings coaxially attached to the said conduit at spaced intervals alongthe length thereof between said spaced annular closures, each of saidrings having a concentric circular row of openings extending through theopposed faces thereof and said rings being so aligned that radiallycorresponding openings in said rings lie in substantially straight linessubstantially parallel to the longitudinal axis of said conduit; and aplurality of electrical insulating members affixed to said rings, saidmembers having longitudinal openings in register with the openings insaid rings, and the longitudinal traverses of the said heating elementpassing through said openings in said insulating members and said rings.

5. A well heater in accordance with claim 4 wherein the means foraifixing the said heating element with respect to said conduit comprisesupper and lower sleeves affixed to each of the longitudinal traverses ofsaid heating element respectively immediately above and immediatelybelow one of said insulating members located at the approximatemid-point of said longitudinal traverse.

6. A well heater for use in oil wells comprising an imperforate conduitadapted to be coupled to the well tubing; a coaxial tubular shell ofsubstantially larger diameter than said conduit; upper and lower annularclosures providing a fluid-tight seal between said conduit and saidshell; a plurality of relatively flat rings each provided with aconcentric circular row of openings extending through its opposed faces,said rings being affixed to said conduit at spaced intervals along thelength thereof between said annular closures in planes substantiallyperpendicular to the longitudinal axis of said conduit and being soaligned that radially corresponding openings lie in substantiallystraight lines substantially parallel to the longitudinal axis of saidconduit; an electrically nonconductive member carried in each of saidopenings, each of said members having a longitudinal opening extendingtherethrough and in register with each of said openings in said rings;an electrically resistive conductor carried in the openings inlongitudinal rows of said non-conductive members, said conductor therebytaking the form of a serpentine with relatively long traversessubstantially parallel to the longitudinal axis of said conduit; upperand lower sleeves attached to each of the longitudinal traverses of saidconductor respectively immediately above and immediately below one ofsaid non-conductive members located at the approximate mid-point of saidtraverses; and electrically conductive means for supplying electriccurrent to said conductor from an exterior source.

7. A well heater in accordance with claim 6 wherein the saidelectrically conductive means comprises means for electricallyconnecting one end of said resistive conductor to said conduit and aninsulated conductor electrically connected to the other end of saidresistive conductor and passing to the exterior of the heater via afluid-tight seal.

8. A well heater in accordance with claim 6 containing a particulateheat-conducting electrical-insulating refractory solid in the annularspace between said conduit and said shell, in contact with saidelectrically resistive conductor, said conduit and said shell.

9. An electric heater for use in wells comprising an imperforate conduitadapted to be coupled to the well tubing; a coaxial tubular shell ofsubstantially larger diameter than said conduit; upper and lower annularclosures providing a fluid-tight seal between said conduit and saidshell; a plurality of spiders having radial arms and afiixed to saidconduit at spaced intervals along the length thereof between saidannular closures in planes substantially perpendicular to thelongitudinal axis of said conduit, said spiders being so aligned thatthe outer extremities of their corresponding radial arms lie onsubstantially straight lines substantially parallel to the longitudinalaxis of said conduit; an electrically non-conductive member carried oneach of the radial arms of each of said spiders; an electricallyresistive conductor supported along its length on longitudinal rows ofsaid nonconductive members, said conductor thereby taking the form of aserpentine with relatively long traverses substantially parallel to thelongitudinal axis of said conduit; upper and lower sleeves attached toeach of the longitudinal traverses of said conductor respectivelyimmediately above and immediately below one of said nonconductivemembers located at the approximate mid-point of said traverses; andelectrically conductive means for supplying electric current to saidconductor from an exterior source.

10. An electric heater for use in wells comprising an imperforateconduit adapted to be coupled to the well tubing; a coaxial tubularshell of substantially larger diameter than said conduit; upper andlower annular closures providing a fluid-tight seal between said conduitand said shell; a plurality of stand-off insulators aflixed at theirbases to said conduit so as to extend into the annular space betweensaid conduit and said shell in radial disposition and in a plurality ofplanes perpendicular to the longitudinal axis of said conduit and spacedat intervals along the length of said conduit between said annularclosures; an electrically resistive conductor supported along its lengthon longitudinal rows of said insulators, said conductor thereby takingthe form of a 8 serpentine with relatively long traverses substantiallyparallel to the longitudinal axis of said conduit; means for rigidlyafiixing said conductor to-said insulators at approximately themid-point of each of said traverses; and electrically conductive meansfor supplying electric current to said conductor from an exteriorsource.

11. A well heater in accordance with claim 1 containing a particulateheat-conducting electrical-insulating refractory solid in the annularspace between said conduit and said shell and in contact with saidheating element, said conduit and said shell; and a heat-conductingelectrical-insulating liquid filling the spaces between the particles ofsaid solid.

12. A well heater in accordance with claim 6 containing a particulateheat-conducting electrical-insulating refractory solid in the annularspace between said conduit and said shell and in contact with saidheating element, said conduit and said shell; and a heat-conductingelectrical insulating liquid filling the spaces between the particles ofsaidsolid.

13. A well heater in accordance with claim 9 containing a particulateheat-conducting electrical-insulating refractory solid in the annularspace between said conduit and said shell and in contact with saidheating element,

said conduit and said shell; and a heat-conducting electrical-insulatingliquid filling the spaces between the particles of said solid.

References Cited in the file of this patent UNITED STATES PATENTS1,457,690 Brine June 5, 1923 1,842,972 Ipsen et al Jan. 26, 19322,076,669 Redfield et a1 Apr. 13, 1937 2,632,836 Ackley Mar. 24, 19532,647,196 Carpenter et al. July 28, 1953

